Cable systems, for example underground cable systems, including power (energy) cables or data communications and telecommunications cables and in particular cable systems passing through water, are very sensitive to damage and destruction wherein water penetrates into the cable core and spreads along the cable. Considerable damage and complete failures of the functionality of the cable systems can be caused thereby.
Many cable products are endowed with one or more water-blocking protective layers for protection against the penetration and the spreading of water. For example, watertight sheaths, water-blocking layers, which are inserted between a central core and a core or sheath, water-blocking yarns, water-blocking tapes and combinations thereof are used for this. Such water-blocking protective devices act against penetration of water in the direction of areas of the central core, which for example contains optical fibers, and spreading of the water along the cable axes which would lead to damage of further sections of the cable.
Layered water-blocking tapes have the disadvantage that during cable production the active water-blocking compounds can sometimes be partially lost for example by mechanical abrasion. In order to prevent this, water-blocking tapes are often sealed or bonded with adhesives and adhesives. However, such adhesives and adhesives are disadvantageous, since they inhibit the swelling action and swelling rate of the water-blocking compounds and thus impair the water-blocking properties of the tapes. In addition, the use of binders increases the weight of the coated materials. Water-soluble binders and adhesives are normally used. As a result of this, the binder dissolves on contact with water and the water-blocking compound begins to swell. As a result, the water-blocking agent loses its attachment to the substrate and can thus be flushed out in the event of damage to the cable and under water pressure can migrate along cavities in cables.
DE 4134370C1 describes a swellable cable band layer, consisting of a nonwoven which is coated with super-absorbers in powder form by means of an adhesive. In this publication, the problem of powder attachment by means of a binder is discussed with regard to the free swellability or degree of swelling for cable use. A compromise between powder attachment and swellability is proposed.
Consequently it would be desirable to obtain a textile fabric with which the spreading of water in cables can be effectively prevented. The textile fabric should as far as possible do without adhesives and/or adhesives, in order to maximize the swelling action and swelling rate. Further, it would be desirable for the textile fabric to have a low weight and sufficient flexibility for use in a wide variety of cable configurations.
Also known is the use of fibers which consist of super-absorbers (SAP fibers). However, a disadvantage with these fibers is that in the swelled state they display low gel strength. The SAP fibers are also not firmly bound in or around the matrix fibers. Under hydrostatic pressure, the gel migrates very rapidly along cavities in the cable.
From DE 000069609828 T2, a water-blocking composite material is known, comprising a substrate which is coated with a mixture of an irradiation-polymerized compound and a compound swellable in water. As substrates, fibers (glass fibers, yarns, optical fibers), wires or rods (e.g. components subject to cable drawing) or tubes (e.g. polymer cable sheathings or buffer sheaths) or other articles are used. These are endowed with the swellable compound and a coating of variable thickness is thus formed. With the formation of coatings as described in this publication, it is disadvantageous that such composite materials are only to a limited extent suitable for preventing the spreading of water in the longitudinal direction along the cable. In particular, the composite materials have a rather low swelling—and thus blocking—rate. In addition, no firm bonding to the substrate can be achieved through the application of the swellable compound as a coating. This leads to detachment of the swellable compound during production and/or in use, for example on contact with water.